The present invention relates to a rotary magnetic recording medium capable of revolution such as a magnetic disc, etc. and a process for preparing the same, and particularly to a rotary magnetic recording disk with a lubricant of high reliability and a process for preparing the same.
Generally, a rotary magnetic recording medium such as a magnetic disk, etc. is in a structure comprising a substrate, a magnetic layer laid thereon and, if necessary, a protective layer laid on the magnetic layer. Such a magnetic recording medium suffers from wear by occasional contact with a magnetic head floating over the surface of the magnetic recording medium during the recording and reproduction, or from additional wear by dust generated by the wear caused by the occasional contact. The wear may lead to the protective layer or the magnetic layer being scraped away, resulting in a decrease in the recording or reproduction characteristics. To cope with this problem, it has been so far proposed and used to provide a lubricating film layer on the surface of the magnetic recording medium to give a wear resistance to the medium.
For example, it was proposed to use perfluoropolyether as a lubricant to improve the sliding characteristics (U.S. Pat. Nos. 3,778,308; 3,919,719; 4,268,556), or to use perfluoropolyether with an improved adhesiveness with respect to the lubricating film layer and the surface of magnetic recording medium by introducing polar groups such as --CH.sub.2 OH, --COOR, --CONHR, --COOCH.sub.3, etc. and various functional groups to the terminal ends of perfluoropolyether [Japanese Patent Applications Kokai (Laid-open) Nos. 61-155345, 61-113126, 62-270019 and 2-101626]. As a result of these proposed improvements, a lubricating film layer of higher reliability has been available.
Generally, it is not satisfactory that the lubricating film layer for use in a rotary magnetic recording medium such as a magnetic disk, etc. have distinguished lubricating characteristics. That is, since a magnetic disk as a rotary magnetic recording medium is used for many revolutions over a long period of time, the lubricant will be scattered by a centrifugal force, etc. during the long this time, resulting in deterioration of the reliability of the lubricating film layer. To solve this problem, it has been attempted to use a lubricant having a high viscosity or a lubricant having functional groups, which have a good adhesiveness to the disk surface, at the terminal ends of one lubricant molecule. The characteristics have been improved to some extent by these lubricants, but satisfactory characteristics that can meet the demands of prolonged use have not been obtained yet.